Fluid responsiveness predicted by noninvasive Bioreactance-based passive leg raise test

Abstract

To study the feasibility of predicting fluid responsiveness (FR) by passive leg raising (PLR) using a Bioreactance-based noninvasive cardiac output monitoring device (NICOM). This prospective, two-center study included 75 consecutive intensive care unit (ICU) adult patients immediately after cardiac surgery. NICOM was used to continuously record cardiac output (CO) at baseline, during a PLR, and then during a 500 ml i.v. rapid colloid infusion. We estimated the precision of NICOM at baseline to derive the least minimum significant change (LMSC) in CO. We studied the predictability of PLR for FR by systematic analysis of different categorizations of PLR and FR, based on percentage change in CO (from 0 to 20%). The LMSC was 8.85%. CO was 4.17 ± 1.04 L min⁻¹ at baseline, 4.38 ± 1.14 L min⁻¹ during PLR, 4.16 ± 1.08 L min⁻¹ upon return to baseline, and 4.85 ± 1.41 L min⁻¹ after fluid infusion. The change in CO following fluid bolus was highly correlated with the change in CO following PLR: y = 0.91x + 4.3, r = 0.77. The Pearson correlation coefficient showed that the best pair of thresholds was found for PLR ≥ 0% predicting FR ≥ 0%. Using this pair of thresholds, PLR had 88% sensitivity and 100% specificity for predicting FR. When we restricted the analysis to change in CO > LMSC, the best pair of thresholds was obtained for PLR > 9% predicting FR > 9%. Using this pair of thresholds, PLR sensitivity was reduced to 68% and specificity to 95%. In this specific population of patients, it is clinically valid to use the bioreactance-based NICOM system to predict FR from changes in CO during PLR.